The present invention relates in general to downhole well machinery powered by power fluid from the surface and which lubricates bearings of the machinery from a branch stream of the fluid that has been cleansed by a cleaner of the machine. In particular, the present invention relates to turbo-machines with centrifugal cleaners for separating solids from fluids downhole in wells and to a centrifugal cleaner that provides a solid-free lubricant stream from power fluid, which lubricant stream loads a thrust bearing runner and lubricates journal bearings and journals of pump and turbine stages, with the turbine stages being powered by the balance of the power fluid.
Downhole turbine machinery for use in petroleum and water wells is known. Turbine stages of the machinery powered by power fluid from the surface of the wells drive staged axial flow pumps that in turn force well fluid to the surface. The turbo-machinery operates at incredible speeds and is subject to considerable pressure differentials. Speeds on the order of 65,000 RPM can be experienced. Power fluid pressure differentials of as much as 280 Kg/cm.sup.2 exist.
These very high speeds result in very severe bearing conditions. Under these conditions small particles in lubricant erode bearings rapidly. High pressure differentials translate into the same problem by producing high lubricant stream velocities across bearing surfaces, and entrained tiny particles in the lubricant have enormous erosive power.
To avoid excessive turbine blade wear, power fluid is maintained comparatively free of solid, abrasive materials. Usually, the power fluid receives treatment at the surface to remove solid materials. Power fluid, therefore, appears attractive as a lubricant.
The turbine blades can stand a modest solid content in the power fluid. The turbo-machine's bearings, however, cannot tolerate solids concentrations acceptable by the turbine blades. Removal of solids at the surface to an acceptable concentration for lubrication purposes is wasteful. The capacity of the solid removal equipment with adequate solid removal for lubrication must be large enough to handle the flow rate for the entire power fluid stream, including that which powers the turbines, unless a separate line is run for lubricant. The running of a separate line for lubricant from the surface to the bottom hole location is obviously not desirable for it complicates well plumbing.
Spent power fluid exhausted from downhole turbo-machines may be circulated in a closed power fluid system whereby the fluid returns to the surface in a separate tubing string from other strings passing fluids into and from the well. Alternatively, in an open system spent power fluid can be discharged into well fluid to form a production fluid stream. Typically, in this instance, the production fluid stream of both spent power fluid and well fluid passes up an annulus between the well casing and the power fluid supply string. Production fluid can, however, travel up a tubing string of its own. In the open system, power fluid picks up solids from the well fluid. In both open and closed systems, power fluid streams also pick up solid particles in the course of travel through the various tubing strings.
Accordingly, it is desirable to provide in effect two power fluid streams, one having an extremely low solids content for lubricant purposes, and one having a higher permissible solids content for driving the turbines and to originate the clean stream downhole.